450 Formula Upper Extremity Practice Exam 2026 - Free Practice Questions and Study Guide

Swan neck deformity arises when the extensor mechanism around the finger loses its normal restraint at the PIP joint, allowing the PIP to hyperextend. The volar plate at the PIP normally checks hyperextension; if it’s weak or torn, the PIP drifts into hyperextension and the extensor mechanism shifts in a way that the DIP is driven into flexion. This pattern is most commonly due to volar plate weakness or injury at the PIP, sometimes with metacarpophalangeal joint subluxation contributing to the imbalance.

Other options don’t fit the pattern: carpal tunnel is a nerve compression issue with no direct impact on finger joint alignment; a humerus fracture is in the upper arm and doesn’t create this finger deformity; a distal phalanx avulsion causes a mallet finger, which presents as DIP flexion with an unaffected or differently aligned PIP.